The present invention relates generally to manned and unmanned aircraft adapted for short take-offs and landings (STOL). More particularly, the present invention deals with a STOL aircraft having a variable-area, variable pitch, deployable wing. In addition, the present invention pertains to a method of operating an aircraft to achieve STOL performance.
Through the years various approaches have been used by aircraft designers and engineers to reduce the length of the ground roll during take-offs and landings. Reduction of ground roll length is desirable for many reasons, only a few of which will be discussed here. For example, shorter runways can be usedxe2x80x94thus many otherwise marginal areas can be serviced. Conversely, heavier aircraft gross weights can be used with existing runwaysxe2x80x94thus permitting larger and more profitable aircraft to be used.
Perhaps the epitome of STOL aircraft are rotary wing aircraft, e.g., helicopters, and directable thrust aircraft, e.g., the Harrier, which can land and take-off vertically. Both the rotary wing aircraft and the directable thrust aircraft require a more complex control system than conventional aircraft. As a result, pilots of such aircraft need special training.
Some of the more conventional approaches to STOL aircraft performance involve the use of wing leading-edge treatments, e.g., slats, and wing trailing-edge treatments, e.g., large flaps, to improve the aerodynamic performance of the wing at low speed operation.
Other nuances to improve aerodynamic performance include use of high aspect ratio wing designs, and wing tip fences. Here again, the emphasis is upon improving the aerodynamics of the lifting surfaces so that greater lift is acquired for a given speed thereby reducing the ground roll or increasing the take-off gross weight.
Another approach to improved STOL performance involves variable position wings. In one position the wings are adapted for lower speed flight, whereas in a second position the wings are adapted for higher speed flightxe2x80x94an example of an aircraft with such variable position wings is the F-111.
The common thread to the known approaches to STOL performance is improved aerodynamic performance of the fixed wing. Only limited improvements can be anticipated without a fresh view of the problem and potential solutions. The present invention heralds a different approach to the desirable characteristic of STOL performance.
A general object of the present invention is to enhance V/STOL aircraft performance by changing the emphasis from simple aerodynamic enhancements.
This and many other objects and advantages are attained in an aircraft structure having a fuselage, a rigid wing, and thrust means, by further providing a deployable wing operably connected to the fuselage so that its angle of attack can be adjusted to a value substantially exceeding the conventional stall angle for the wing-fuselage assembly. In the foregoing manner, the deployable wing operates as a reaction surface with aerodynamic properties.
To permit adjustment of the lift generated by the deployable wing, a mechanism is provided to adjust its angle of attack. In this way, as the aircraft attains a speed and altitude where the auxiliary lift of the deployable wing is no longer needed, the auxiliary lift can be reduced by reducing the angle of attack so that the deployable wing can be stowed. Conversely, when the aircraft begins a landing, deployment of the wing can be controlled so that there is no change in lift until needed.
So that the deployable wing can be stowed, a mechanism for changing the area of the deployable wing is also provided. Accordingly, the wing area can be varied from 100% of full deployment to its fully retracted value which may be 0% or another small value, preferably not greater than about 10% of the full deployment area.
In one embodiment, the deployable wing may have the configuration of a delta wing kite having a central spar about which the wing can be furled and unfurled.
In another embodiment, the deployable wing may comprise a plurality of nested airfoil sections which extend and retract through the trailing edge of the next larger section.
In order to help directionally control the aircraft structure, propulsion may be provided with a Q-fan engine arrangement. Thus, the thrust generated by the engine is further aligned with a longitudinal axis of the structure.